1. Field of the Invention
The present invention relates to an additive for a photoresist composition for a resist flow process, and a photoresist composition comprising the same. In particular, the present invention relates to a photoresist composition comprising an additive which lowers the glass transition temperature of the photoresist polymer, and a method for forming a contact hole using the same.
2. Description of the Background Art
Recently, semiconductor devices have been highly integrated. It is difficult to form a contact hole having a high resolution in lithography process. Currently, a contact hole patterning limit of KrF lithography is about 0.18 μm. Resist flow is a processing technology for forming a fine contact hole which exceeds the resolution of the exposing device.
The resist flow process has recently made remarkable developments and so that it is now used in mass production processes. The technology generally involves an exposure process and a development process. This process forms a photoresist contact hole having a resolution equal to that of the exposing device. The process also includes heating the photoresist to a temperature higher than the glass transition temperature of the photoresist which causes the photoresist to flow. The contact hole gets smaller by the flow of photoresist until a fine contact hole necessary for the integration process is obtained.
Most of the KrF resists can be flow processed, though having different profiles after the flow process. That is, the KrF resist mainly containing polyvinylphenol consists of a structure having appropriate Tg for the flow. However, a resist used for ArF lithography has so high Tg that it cannot be flow processed. Especially, cycloolefine resists have a Tg over about 200° C., and thus is not suitable for the resist flow process. An appropriate temperature for the resist flow process ranges between the Tg of the photoresist polymer and a decomposition temperature (Td) where the polymer starts to be decomposed. Therefore, the polymer having high Tg cannot be used for a resist flow because the Tg and Td have only a slight difference. Therefore, there is a need for a modified resist material with a suitable disparity between the Tg and Td thereby making it suitable for resist flow processing.